System and method for three-dimensional reconstruction of an artery

ABSTRACT

A method and system for imaging an artery contained in an arterial tree. A microprocessor generates a three-dimensional reconstruction of the arterial tree from two or more angiographic images obtained from different perspectives. The orientation of the axis of the artery in the arterial tree is then determined, and a perspective of the artery perpendicular to the axis of the artery is determined. A three dimensional reconstruction of the artery from angiographic images obtained from the determined perspective is then generated.

FIELD OF THE INVENTION

[0001] The present invention relates to medical devices, and morespecifically to such devices for use in angiography.

BACKGROUND OF THE INVENTION

[0002] Stenosis of an artery refers to narrowing of the artery lumen dueto plaque formation on the interior wall of the artery. The severity ofthe stenosis is the fraction of the cross-sectional area of the lumenthat is occluded by plaque. Since narrowing is often asymmetrical aboutthe axis of the artery, in order to assess the severity of a stenosis,it is necessary to obtain at least two, and preferably more, imagesperpendicular to the artery axis from orthogonal perspectives.

[0003] In angiography, the arterial lumen is filled with a radio-opaquesubstance and X-ray images of the arterial tree are obtained fromdifferent perspectives. Selection of these perspectives is partlyarbitrary and partly a process of trial and error once a stenosis hasbeen observed. However, the overall number of images that can beobtained is limited by time, safety and cost. Usually four to sevenprojections for the left coronary arterial system and two to four forthe right coronary artery are obtained. The operator assesses theseverity of the stenosis either on the basis of visual examination ofthe images or by computer analysis of a single image. Since theseprojections are in general not perpendicular to the arterial axis,estimation of stenosis severity and its length from these images isusually not accurate.

SUMMARY OF THE INVENTION

[0004] It is therefore an object of the invention to provide a moreaccurate process and system for computer reconstruction of an arteryfrom discrete images of the artery.

[0005] Such an objective is realized in accordance with a first aspectof the invention by a system comprising means for obtainingtwo-dimensional angiographic images of arteries, and a microprocessorfor processing the images. The images may be obtained, for example, byX-ray angiography or by ultrasound.

[0006] In accordance with a second aspect of the invention, there isprovided a process for obtaining two or more angiographic images of anarterial tree. The images preferably include two images taken fromperpendicular perspectives. In the case of the coronary arterial tree,all images are preferably obtained when the heart is in the same state,for example, diastole. A three dimensional (3D) reconstruction of thearterial tree is generated by the microprocessor from the images bymethods known in the art. Methods of generating a 3D reconstruction ofan arterial tree from discrete images can be found, for example, inanyone of the following references all of which are included herein intheir entirety by reference: Faugeras, O. D., Mass. Inst. Tech. 1993;Garreau, et al., EEE Trans Med Imag 10(2):122-131; Grosskopf, S,Dissertation, Technical University of Berlin, 1994; and Hildebrand andGrosskopf, in Proc. Comp. Assisted Radiology CAR 95 conference, BerlinSpringer, pp 201-207, 1995. The arterial tree may be, for example, thecoronary arterial tree, the renal arterial tree, the pulmonary arterialtree, the cerebral arterial tree, or the hepatic arterial tree.

[0007] The 3D reconstructed arterial tree may be represented on adisplay screen using pseudo 3D effects such as directional lighting andshading. In a preferred embodiment, the reconstructed tree is presentedas a stereoscopic pair of images to be viewed by the operator using astereoscopic viewer. The reconstruction may be manipulated on the screenby the operator, allowing him, for example, to zoom in on a specificregion or to rotate the reconstructed artery on the screen to obtain adesired perspective.

[0008] An artery, for example, a stenotic or aneurotic artery present inany of the obtained angiographic images may be detected by analysis ofthe images by the microprocessor or by visual examination of the imagesby the operator. The microprocessor determines the orientation of theaxis of the artery in the 3D reconstruction of the arterial tree. Themicroprocessor then calculates two or more perspectives of the arteryperpendicular to the arterial axis. Preferably, two orthogonalperspectives are determined. If images of the selected artery have notalready been obtained approximately from the calculated perspectives,the operator obtains angiographic images of the artery from theseperspectives and the microprocessor then constructs a 3D reconstructionof the artery from the angiographic images by methods known in the art.The invention thus allows an operator to obtain images of the arteryfrom orthogonal perspectives more rapidly than is possible by prior artmethods of trial and error. This allows a smaller radio-opaque dosage tothe patient and a reduced exposure of the patient and the is operator toX-rays.

[0009] The microprocessor may apply meteorological tools to thereconstructed artery. In the case of a stenotic artery, themicroprocessor may provide accurate quantitative assessment of theextent and length of the stenosis. The severity of a stenosis may bedescribed quantitatively, for example, by the fraction of the arteriallumen occupied by plaque.

[0010] The 3D reconstructed artery may be represented on a displayscreen using pseudo 3D effects such as directional lighting and shading.In a preferred embodiment, the reconstructed artery is presented as astereoscopic pair of images to be viewed by the operator using astereoscopic viewer. The reconstruction may be presented to the operatorembedded in the 3D reconstruction of the entire arterial tree. Thereconstruction may be manipulated on the screen by the operator,allowing him, for example, to zoom in on a specific region or to rotatethe reconstructed artery on the screen to obtain a desired perspectiveof the stenosis including a perspective showing maximal narrowing or across section of the artery.

[0011] Thus, in its first aspect the invention provides a system forimaging an artery contained in an arterial tree, the artery having anaxis, the system comprising:

[0012] a a microprocessor configured to

[0013] aa generate a three-dimensional reconstruction of the arterialtree from two or more angiographic images of the arterial tree obtainedfrom different perspectives;

[0014] ab determine an orientation of the axis of the artery in thearterial tree;

[0015] ac determine from the three-dimensional reconstruction of thearterial tree at least one perspective of the artery perpendicular tothe axis of the artery; and

[0016] ad generate a three dimensional reconstruction of the artery fromangiographic images obtained essentially from the determined at leastone perspective.

[0017] In its second aspect, the invention provides a method for imagingan artery contained in an arterial tree, the artery having an axis, themethod comprising the steps of:

[0018] a generating a three-dimensional reconstruction of the arterialtree from two or more angiographic images of the arterial tree obtainedfrom different perspectives;

[0019] b determining an orientation of the axis of the artery in thearterial tree;

[0020] c determining from the three-dimensional reconstruction of thearterial tree at least one perspective of the artery perpendicular tothe axis of the artery; and

[0021] d generating a three dimensional reconstruction of the arteryfrom angiographic images obtained essentially from the determined atleast one perspective.

[0022] In its third aspect, the invention provides a method fordiagnosing stenosis in an arterial tree in an individual, the methodcomprising the steps of:

[0023] a generating a three-dimensional reconstruction of the arterialtree from two or more angiographic images of the arterial tree obtainedfrom different perspectives;

[0024] b detecting in the three-dimensional reconstruction of thearterial tree a stenotic artery, the stenotic artery having an axis;

[0025] c determining an orientation of the axis of the stenotic artery;

[0026] d determining from the three-dimensional reconstruction of thearterial tree at least one perspective of the stenotic arteryperpendicular to the axis of the artery;

[0027] e generating a three dimensional reconstruction of the arteryfrom angiographic images obtained essentially from the determined atleast one perspective; and

[0028] f analyzing the three-dimensional reconstruction of the artery.

[0029] In its fourth aspect, the invention provides a program storagedevice readable by machine, tangibly embodying a program of instructionsexecutable by the machine to perform method steps for imaging an arterycontained in an arterial tree, the artery having an axis, said methodsteps comprising:

[0030] a generating a three-dimensional reconstruction of the arterialtree from two or more angiographic images of the arterial tree obtainedfrom different perspectives;

[0031] b determining an orientation of the axis of the artery in thearterial tree;

[0032] c determining from the three-dimensional reconstruction of thearterial tree at least one perspective of the artery perpendicular tothe axis of the artery; and

[0033] d generating a three dimensional reconstruction of the arteryfrom angiographic images obtained essentially from the determined atleast one perspective.

[0034] In its fifth aspect, the invention provides a computer programproduct comprising a computer useable medium having computer readableprogram code embodied therein for imaging an artery contained in anarterial tree, the artery having an axis, the computer program productcomprising

[0035] a computer readable program code for causing the computer togenerate a three-dimensional reconstruction of the arterial tree fromtwo or more angiographic images of the arterial tree obtained fromdifferent perspectives;

[0036] b computer readable program code for causing the computer todetermining an orientation of the axis of the artery in the arterialtree;

[0037] c computer readable program code for causing the computer todetermine from the three-dimensional reconstruction of the arterial treeat least one perspective of the artery perpendicular to the axis of theartery; and

[0038] d computer readable program code for causing the computer togenerate a three dimensional reconstruction of the artery fromangiographic images obtained essentially from the determined at leastone perspective.

[0039] In its sixth aspect, the invention provides a program storagedevice readable by machine, tangibly embodying a program of instructionsexecutable by the machine to perform method steps for diagnosingstenosis in an arterial tree in an individual, said method stepscomprising:

[0040] a generating a three-dimensional reconstruction of the arterialtree from two or more angiographic images of the arterial tree obtainedfrom different perspectives;

[0041] b detecting in the three-dimensional reconstruction of thearterial tree a stenotic artery, the stenotic artery having an axis;

[0042] c determining an orientation of the axis of the stenotic artery;

[0043] d determining from the three-dimensional reconstruction of thearterial tree at least one perspective of the stenotic arteryperpendicular to the axis of the artery;

[0044] e generating a three dimensional reconstruction of the arteryfrom angiographic images obtained essentially from the determined atleast one perspective; and

[0045] f analyzing the three-dimensional reconstruction of the artery.

[0046] In its seventh aspect, the invention provides a computer programproduct comprising a computer useable medium having computer readableprogram code embodied therein for diagnosing stenosis in an arterialtree in an individual the computer program product comprising:

[0047] a computer readable program code for causing the computer togenerate a three-dimensional reconstruction of the arterial tree fromtwo or more angiographic images of the arterial tree obtained fromdifferent perspectives;

[0048] b computer readable program code for causing the computer todetect in the three-dimensional reconstruction of the arterial tree astenotic artery, the stenotic artery having an axis;

[0049] c computer readable program code for causing the computer todetermine an orientation of the axis of the stenotic artery;

[0050] d computer readable program code for causing the computer todeterme from the three-dimensional reconstruction of the arterial treeat least one perspective of the stenotic artery perpendicular to theaxis of the artery;

[0051] e computer readable program code for causing the computer togenerate a three dimensional reconstruction of the artery fromangiographic images obtained essentially from the determined at leastone perspective; and

[0052] f computer readable program code for causing the computer toanalyze the three-dimensional reconstruction of the artery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to understand the invention and to see how it may becarried out in practice, a preferred embodiment will now be described,by way of non-limiting example only, with reference to the accompanyingdrawings, in which:

[0054]FIG. 1 shows a cross-sectional view and two projections of astenotic artery;

[0055]FIG. 2 is block diagram showing an embodiment of the system of theinvention according to one embodiment of the invention; and

[0056]FIG. 3 is a flow chart diagram of the process of constructing athree-dimensional reconstruction of a stenotic artery.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0057] Referring first to FIG. 1, a cross section 100 of a stenoticartery is shown. The artery has a circular lumen that is partiallyoccluded by plaque 105. In angiography, the unoccluded portion of thelumen 110, (indicated in FIG. 1 by cross-hatching) is filled with aradio-opaque substance. 115 a and 115 b are two longitudinal projectionsof the radio-opacity of the artery as would be obtained in angiography.The projections 115 a and 115 b are from orthogonal perspectives asindicated by the broken lines 120 a and 120 b. In the projection 115 athe stenosis appears to be non-critical. The projection 115 b, on theother hand, shows maximal narrowing of the arterial lumen indicatingthat the stenosis is in fact critical.

[0058] In FIG. 2, a block diagram of a preferred embodiment of thesystem of the invention is shown. An X-ray source 200 and an X-raydetector 205 are used to obtain angiographic images of an individual210. An X-ray beam 212 is produced by the X-ray source 200 and isdetected by the detector 205 after having passed through the body of theindividual 210. The analog signal 215 produced by the detector 205 isconverted into a digital signal 225 by analog-to-digital converter 220.The digital signal 225 is inputted into a microprocessor 230 and storedin a memory 240. An analog ECG signal 270 may also be simultaneouslyobtained from the individual 210. The analog ECG signal 270 is convertedinto a digital signal 280 by analog-to-digital converter 275 and thedigital ECG signal 280 is inputted to the microprocessor 230 and storedin the memory 240. The detector signal 225 and the ECG signal 280 aresynchronized by the microprocessor 230. An operator input 250, that maybe, for example, a key board or a computer mouse, is used to allow anoperator to input instructions to the microprocessor 230. A display 255is used to display images either in real-time or images called up fromthe memory 240.

[0059] The orientation of the X-ray beam 212 and the plane 260 of theindividual's body may be selected by the operator in order to produce animage of an arterial tree of the individual, for example, the coronaryartery tree, from a desired perspective. The operator inputs the desiredperspective into the microprocessor 230 by means of operator input 250.The microprocessor 230 then brings the X-ray source 200 and the detector205 into the required orientation by activating a mechanism (not shown)that moves the X-ray source and the detector into the desiredorientation relative to the individual's body, as is known in the art.

[0060] The microprocessor 230 is programmed to generate a 3Dreconstruction of the arterial tree based upon the obtained images. The3D reconstruction of the arterial tree may be represented on display 255using pseudo 3D effects such as directional lighting and shading. In apreferred embodiment, the reconstructed tree is presented as astereoscopic pair of images on display 255 to be viewed by the operatorusing a stereoscopic viewer. The 3D reconstruction of the arterial treemay be manipulated on the display 255 by the operator by means ofoperator input 250, allowing him, for example, to zoom in on a specificregion or to rotate the reconstruction on the display to obtain adesired perspective.

[0061] An artery of interest, for example, a stenotic artery, in animage or in the 3D reconstructed tree is selected by the operator ordetected by the microprocessor, for example, by gray level analysis asis known in the art. For example, an image or the reconstructed tree maybe displayed on the display 255, and an artery selected by the operatorby means of input 250. The microprocessor determines from the 3Dreconstruction of the arterial tree the angular orientation of theselected artery. The microprocessor then calculates two or moreperspectives perpendicular to the axis of the selected artery. Theperspectives preferably include two orthogonal perspectives. If imagesof the selected artery have not already been obtained approximately fromthe calculated perspectives, the operator obtains such images. Themicroprocessor 230 is programmed to reconstruct a 3D image of theselected artery based upon these images. The 3D reconstruction of theartery may be represented on display 255 using pseudo 3D effects such asdirectional lighting and shading. In a preferred embodiment, thereconstruction is presented as a stereoscopic pair of images on display255 to be viewed by the operator using a stereoscopic viewer. Thereconstruction of the artery may be presented to the operator embeddedin the 3D reconstruction of the entire arterial tree.

[0062] The 3D reconstruction of the artery may be manipulated on thedisplay 255 by the operator by means of operator input 250, allowinghim, for example, to zoom in on a specific region or to rotate thereconstruction on the display to obtain a desired perspective, includingan optimal perspective or a cross-section.

[0063] The microprocessor may optionally be programmed to determinequantitative and qualitative parameters of a stenosis based upon the 3Dreconstruction. Such parameters may include, for example, the length andseverity of a stenosis.

[0064] Referring now to FIG. 3, a flow chart is shown describing apreferred embodiment of the process of the invention. At step 310 theoperator obtains at least two angiographic images of an arterial tree ofthe individual 210 from different, preferably perpendicular,perspectives. The images are displayed on the display 255 in step 315,and a 3D reconstruction of the arterial tree is generated from theobtained images 318. The 3D reconstruction may optionally be displayedon the display 255. The obtained angiographic images or the 3Dreconstructed tree is examined for arteries of interest, for example,stenotic arteries. The examination may be performed either automaticallyby the microprocessor 230 or by visual examination by the operator (step320). If no artery of interest is detected in any of the images or inthe 3D reconstructed tree the operator decides whether additional imagesare to be obtained from a new perspective (step 330). If at step 330 theoperator decides not to obtain additional images, the process isterminated. If, at step 330 the operator decides to obtain an additionalimage, a perspective is selected and the operator inputs the perspectiveinto the microprocessor 230, and the process then returns to step 315.If in step 320 one or more arteries of interest are observed, an arteryof interest is selected in step 340. In step 345 the microprocessorcalculates two or more perspectives perpendicular to the axis of theselected artery (step 348). The perspectives preferably include twoorthogonal perspectives. If images of the selected artery have notalready been obtained approximately from the calculated perspectives,the operator obtains such images (step 348). In step 350, themicroprocessor updates the 3D reconstruction of the artery. Thereconstructed artery is displayed on the display 255 in step 355together with parameters describing the artery. For example, for astenotic artery, the parameters may include the severity and length ofthe stenosis. The reconstructed artery may be presented to the operatorembedded in the 3D reconstruction of the entire arterial tree. Theoperator may change the display using input 250, for example, byrotating the reconstructed artery on the display 255 so as to change thescale of the reconstruction of the artery or view the reconstructionfrom a desired perspective, including an optimal perspective or across-section. The operator then decides in step 360 whether he wishesto obtain a 3D reconstruction of another artery of interest in thearterial tree. If so, the process returns to step 340. If not,additional images are desired, the process terminates.

[0065] It will also be understood that the system according to theinvention may be a suitably programmed computer. Likewise, the inventioncontemplates a computer program being readable by a computer forexecuting the method of the invention. The invention furthercontemplates a machine-readable memory tangibly embodying a program ofinstructions executable by the machine for executing the method of theinvention.

[0066] In the method claims that follow, alphabetic characters used todesignate claim steps are provided for convenience only and do not implyany particular order of performing the steps.

1. A system for imaging an artery contained in an arterial tree, theartery having an axis, comprising: a a microprocessor configured to aagenerate a three-dimensional reconstruction of the arterial tree fromtwo or more angiographic images of the arterial tree obtained fromdifferent perspectives; ab determine an orientation of the axis of theartery in the arterial tree; ac determine from the three-dimensionalreconstruction of the arterial tree at least one perspective of theartery perpendicular to the axis of the artery; and ad generate a threedimensional reconstruction of the artery from angiographic imagesobtained essentially from the determined at least one perspective. 2.The system of claim 1 wherein the microprocessor is further configuredto display on a display any one or more of an angiographic image, thereconstruction of the arterial tree, or the reconstruction of theartery.
 3. The system of claim 2 further comprising a display configuredto display any one or more of an angiographic image, the reconstructionof the arterial tree, or the reconstruction of the artery.
 4. The systemof claim 1 wherein the microprocessor is further configured to makemeterological measurements on the reconstruction of the arterial tree orthe reconstruction of the artery.
 5. The system according to claim 3wherein the microprocessor is further configured to manipulate an imageon the display.
 6. The system of claim 3 wherein the microprocessor isconfigured to display on the display a view of the three-dimensionalreconstruction of the arterial tree from a selected perspective.
 7. Thesystem of claim 3 wherein the microprocessor is configured to display onthe display a view of the three-dimensional reconstruction of the arteryfrom a selected perspective, such as a cross sectional perspective. 8.The system of claim 3 wherein the three-dimensional reconstruction ofthe artery is displayed on the display embedded in the three-dimensionaldisplay of the arterial tree.
 9. A method for imaging an arterycontained in an arterial tree, the artery having an axis, comprising: agenerating a three-dimensional reconstruction of the arterial tree fromtwo or more angiographic images of the arterial tree obtained fromdifferent perspectives; b determining an orientation of the axis of theartery in the arterial tree; c determining from the three-dimensionalreconstruction of the is arterial tree at least one perspective of theartery perpendicular to the axis of the artery; and d generating a threedimensional reconstruction of the artery from angiographic imagesobtained essentially from the determined at least one perspective. 10.The method of claim 9 further comprising a step of displaying on adisplay any one or more of an angiographic image, the reconstruction ofthe arterial tree, or the reconstruction of the artery.
 11. The methodof claim 9 further comprising a step of making meterologicalmeasurements on the reconstruction of the arterial tree or thereconstruction of the artery.
 12. The method according to claim 10further comprising a step of manipulating an image on the display. 13.The method of claim 10 further comprising a step of displaying a view ofthe three-dimensional reconstruction of the arterial tree from aselected perspective.
 14. The method of claim 10 further comprising astep of displaying on the display a view of the three-dimensionalreconstruction of the artery from a selected perspective, such as across sectional perspective.
 15. The method of claim 14 wherein thethree-dimensional reconstruction of the artery is displayed on thedisplay embedded in the three-dimensional display of the arterial tree.16. The method according to claim 9 further including: e detecting inthe three-dimensional reconstruction of the arterial tree a stenoticartery, the stenotic artery having an axis; and f analyzing thethree-dimensional reconstruction of the artery for diagnosing stenosisin an arterial tree.
 17. The method according to claim 16 wherein thestep of analyzing the three-dimensional reconstruction of the arteryincludes determining the length or severity of the stenosis in thestenotic artery.
 18. The method according to claim 16 or 17 wherein thearterial tree is selected from he group comprising the coronary arterialtree, the renal arterial tree, the pulmonary arterial tree, the cerebralarterial tree, and the hepatic arterial tree.
 19. The method accordingto claim 17 wherein the stenotic artery has a lumen, the lumen has across-section of maximal narrowing, the cross-section of maximalnarrowing has a fraction occluded by plaque, and determining theseverity of the stenosis includes determining the fraction of thecross-section of maximal narrowing occluded by plaque.
 20. A computerprogram comprising computer program code means for performing all thesteps of any one of claims 9 to 19 when said program is run on acomputer.
 21. A computer program as claimed in claim 20 embodied on acomputer readable medium.